CLINICAL SHOCK TOLERABILITY AND EFFECT OF DIFFERENT RIGHT ATRIAL ELECTRODE LOCATIONS ON EFFICACY OF LOW-ENERGY HUMAN TRANSVENOUS ATRIAL DEFIBRILLATION USING AN IMPLANTABLE LEAD SYSTEM

Objectives. The objectives of this study were 1) to evaluate the effec t of different right atrial electrode locations on the efficacy of low energy transvenous defibrillation with an implantable lead system; an d 2) to qualitate and quantify the discomfort from atrial defibrillati on shocks delivered by a clinically relevant method. Background. Biatr ial shocks result in the lowest thresholds for transvenous atrial defi brillation, but the optimal right atrial and coronary sinus electrode locations for defibrillation efficacy in humans have not been defined, Methods. Twenty-eight patients (17 men, 11 women) with chronic atrial fibrillation (AF) (lasting greater than or equal to 1 month) were stu died, Transvenous atrial defibrillation was performed by delivering R cave-synchronized biphasic shocks with incremental shack levels (from 180 to 100 V in steps of 40 V). Different electrode location combinati ons were used and tested randomly: the anterolateral, inferomedial rig ht atrium or high right atrial appendage to the distal coronary sinus, Defibrillation thresholds were defined in duplicate by using the step -up protocol, Pain perception of shack delivery was assessed by using a purpose-designed questionnaire; sedation was given when the shock le vel was unacceptable (tolerability threshold). Results, Sinus rhythm w as restored in 26 of 28 patients by using at least one of the right at rial electrode locations tested, The conversion rate with the anterola teral right atrial location (21 [81%] of 26) was higher than that with the inferomedial right atrial location (8 [50%] of 16, p < 0.05) but similar to that with the high right atrial appendage location (16 [89% ] of 18, p > 0.05). The mean defibrillation thresholds for the high ri ght atrial appendage, anterolateral right atrium and inferomedial righ t atrium were all significantly different with respect to energy (3.9 +/- 1.8 J vs. 4.6 +/- 1.8 J vs, 6.0 +/- 1.7 J, respectively, p < 0.05) and voltage (317 +/- 77 V vs. 348 +/- 70 V vs, 396 +/- 66 V, respecti vely, p < 0.05). Patients tolerated a mean of 3.4 +/- 2 shocks with a tolerability threshold of 255 +/- 60 V, 2.5 +/- 1.3 J. Conclusions. Lo w energy transvenous defibrillation with an implantable defibrillation lead system is an effective treatment for AF. Most patients earn tole rate two to three shocks, and, when the starting shock level (180 V) i s close to the defibrillation threshold, they can tolerate on average a shock level of 260 V without sedation, Electrodes should be position ed in the distal coronary sinus and in the high right atrial appendage to achieve the lowest defibrillation threshold, although other locati ons may be suitable for certain patients. (C) 1997 by the American Col lege of Cardiology.